1. Field of the Invention
The present invention relates to a planetary-gear-type parallel-surface processing machine for performing surface processing such as lapping, polishing, and the like.
2. Description of the Related Art
FIG. 4 is a perspective view showing the main portion of a conventional 4-way-type parallel-surface processing machine, and FIG. 5 is a sectional view thereof. In the figures, numeral 1 denotes an annular lower surface plate rotated by a first drive unit (not shown), numeral 2 denotes carriers each having a toothed surface around the outer periphery thereof, numeral 3 denotes an internal gear rotated by a second drive unit (not shown), numeral 4 denotes a sun gear rotated by a third drive unit (not shown), numeral 5 denotes materials to be processed, numeral 6 denotes columns, numeral 7 denotes a suspension plate 7, numeral 8 denotes a universal joint, numeral 9 denotes an annular upper surface plate, numeral 10 denotes a drive shaft rotated by a fourth drive unit (not shown), and numeral 11 denotes drive keys mounted in the key grooves 10a of the drive shaft 10 for coupling the upper surface plate 9 with the drive shaft 10.
When the parallel-surface processing machine operates, the plurality of carriers 2 are radially disposed on the lower surface plate 1 via meshing engagement thereof with the internal gear 3 and the sun gear 4, and the materials to be processed 5 as workpieces are mounted in the plurality of workpiece holding holes of the carriers 2. Furthermore, the upper surface plate 9, which is suspended like a pendulum by the universal joint 8 via components such as the columns 6, suspension plate 7 and the like, is lowered by a pressure adjustment mechanism such as, for example, an air cylinder or the like (not shown) so as to apply a proper load on the materials to be processed 5 which are mounted on the carriers 2. Furthermore, the drive keys 11 mounted on the upper surface plate 9 are coupled with the drive shaft 10. The key grooves 10a of the drive shaft 10 are disposed vertically so that a drive force can be transmitted from the key grooves 10a of the drive shaft 10 to the drive keys 11 while the drive keys 11 are permitted to move vertically. With this arrangement, the upper surface plate 9 naturally descends by gravity while engaging the materials to be processed 5 even after the drive keys 11 are coupled with key groove 10a of drive shafts 10. A support shaft attached to the universal joint 8 is arranged so as to be rotatable via a bearing (not shown), and the upper surface plate 9 is also rotated by the rotation of the drive shaft 10.
When the materials to be processed 5 are being polished, the lower surface plate 1 and the upper surface plate 9 are rotated in opposite directions while abrasive grains are supplied from an abrasive grain supply hole (not shown) disposed at the upper surface plate 9. Furthermore, the rotation of the internal gear 3 and the sun gear 4 causes the carriers 2, on which the materials to be processed 5 are mounted and clamped between the lower surface plate 1 and the upper surface plate 9, to rotate about their own axes as well as to revolve around the outside of the sun gear 4 so that both surfaces of the materials to be processed 5 are polished. Since the rotations of the lower surface plate 1, the internal gear 3, the sun gear 4, and the upper surface plate 9 are controlled by the first, second, third, and fourth drive units, their rotation speeds are adjusted so that the materials to be processed 5 can be polished optimally. Note that the term "polishing" used here is a generic term which means processing executed using abrasive grains such as lapping, polishing, grinding, and the like. The parallel-surface processing machine shown in FIG. 4 and 5 is referred to as a 4-way-type parallel-surface processing machine because it is composed of elements which perform four motions including the rotation of the lower surface plate 1, the rotation of the upper surface plate 9, the rotation of the carriers 2 about their own axes, and the revolution of the carriers 2 around the sun gear 4.
Recently in the mobile telecommunications industry, since there is a trend toward the use of progressively higher frequencies, it is desired to provide resonators and filters, which are main components of mobile telecommunications equipment, which are suitable for the higher frequencies. These components are typically made of dielectric ceramics such as lead zirconate titanate, lead titanate, etc., in addition to ferroelectric single crystals such as quartz, lithium niobate, lithium tantalate, etc. To permit these components to be used at high frequencies, the thicknesses of the substrates for the resonator and for the filter must be further reduced. However, the following problems arise when the thickness of the substrate is further reduced and the conventional 4-way parallel-surface processing machine is used.
(1) In FIGS. 4 and 5, when the upper surface plate 9 is rotated by coupling the drive keys 11 with the drive shaft 10, the drive keys 11 cannot be moved in the vertical direction because the dynamic frictional forces between the key grooves 10a of the drive shaft 10 and drive keys 11 at the coupling sections are increased by being affected by the inertial force caused by the moment of inertia of the upper surface plate 9. Thus, the upper surface plate 9 cannot be automatically lowered by gravity even if the thickness of the materials to be processed 5 is reduced because it is held by the coupling sections.
(2) The lower surface plate 1 is not maintained in parallel with the upper surface plate 9 due to the displacement of the center of the upper surface plate 9 at which it is supported (center of the universal joint 8) from the center of the three coupling sections where the upper surface plate 9 is coupled with the drive shaft 10 via the drive keys 11.
(3) Therefore, the upper surfaces and the lower surfaces of the materials to be processed 5 cannot be polished in parallel with each other. Furthermore, forces are unevenly applied to the materials to be processed 5 from above and below, depending upon the locations of the materials, whereby the materials 5 to be processed may be chipped or cracked.